1. Industrial Field of the Invention
The present invention relates to a multilayer slide bearing comprising a backing metal of copper alloy and an overlay bearing layer, for use in an internal combustion engine of an automobile.
2. Description of the Prior Art
As a conventional multilayer slide bearing, there is known a bearing in which a bearing layer of an Al-Sn system alloy, an Al-Sn-Si system alloy, an Al-Zn system alloy, an Al-Zn-Si system alloy, a Cu-Pb system alloy, or a Cu-Pb-Sn system alloy is formed on a surface of a backing metal (made of, for example, JIS 3141-SPCC, SAE 1010 or the like). The backing metal used in such kind of slide bearing is generally formed of low carbon steel. On the other hand, a housing of retaining the bearing is formed of cast iron, cast steel, carbon steel or alloy steel. A coefficient of thermal expansion of the housing is approximately similar to that of the backing metal. For the reasons, a gap is hardly defined between the bearing and the housing even when the temperatures thereof increase during operation of the automobile, which results in no problems.
Conventionally, properties of a bearing alloy have mainly been regarded as characteristics of a bearing. As regards a backing metal, the workability and bonding property with respect to the bearing alloy have been regarded as more important than the metallic features of the backing metal.
In recent days, however, applications of aluminum alloy to an engine block or a connecting rod of an internal combustion engine for an automobile tends to increase for achieving fuelsaving purposes and lightweight purposes. In such a case where the aluminum alloy is used for a member of a bearing housing, in a conventional bearing utilizing a backing steel, a difference of coefficients of thermal expansion between the bearing and the housing is considerably large, so that a close-contact relationship between the bearing and the housing is lost when the bearing is heated to a high temperature. Thus, the bearing suffers from damage such as fatigue due to fretting or seizure, and attendant damage. The fretting means damage of two contact surfaces caused when small relative movement is periodically repeated between the surfaces. Particularly, in the connecting rod, not only the bearing but also the connecting rod itself may be broken due to fatigue. As mentioned above, the conventional slide bearing has a problem in fretting resistance. On the other hand, a condition of use of the internal combustion engine becomes severer; that is, the internal combustion engine is operated at a higher speed for a high performance design, which results in a problem that damage such as seizure often occurs at the sliding contact portion.
Moreover, in order to improve an adhesion property of the bearing with respect to the housing at a high temperature or at a high load, a trial has conventionally been made to increase an interference between the bearing and the housing to be assembled with each other. The conventional bearing employing a low carbon steel backing metal is, however, not satisfactory as a member of a bearing assembly because the backing metal is low in strength so that settling occurs in the backing metal when the bearing is assembled in the housing under a high assembling stress exceeding an elastic limit of the backing metal, because a coefficient of thermal conductivity of the backing metal is low and therefore, the heat dissipation capacity is insufficient, or because the backing metal is inferior in anti-seizure property.